L-band Synthetic Aperture Radar: Current and future applications
to Earth sciences
Vertical displacement cross sections
10900

Topo (m)Up--Down (cm)A02016 Kumamoto
earthquake sequence
A

800

-10
-20
0

1

2

3

4 km

20

C
10

700

800

B
C

D

700

Topo (m)Up--Down (cm)

1000

B

20

0

600

-10
-20
0

1

2

3

4 km

500

D

South side
Down

Up

Editorial Board (May 2022)
Editor-in-Chief
Takeshi Sagiya, Nagoya University, Japan

Vice Editors-in-Chief
Masahito Nosé, Nagoya University, Japan

Aitaro Kato, University of Tokyo, Japan

Editors
Koki Aizawa
Hideo Aochi
Pascal Audet
Kiyoshi Baba
Joseph B.H. Baker
Nanan Balan
Stephan Christoph Buchert
Sonia Calvari
Xiaowei ChenPeter Chi
Harold C. Connolly Jr
Phil Cummins
Hao Dong
Guangyu Fu
Hidenori Genda
Aditya Gusman
Tomasz Hadaś
Stuart Henrys
James Hickey
Hauke Hussmann

Mie Ichihara
Hidekatsu Jin
Art Jolly
Shunichi Kamata
Nobuki Kame
Katsuya Kaneko
Ikuo Katayama
Yoko Kebukawa
Kunihiro Keika
Kostas Konstantinou
Alexey Kuvshinov
Juanjo Ledo
Koji Matsuo
Yasunobu Miyoshi
Atsuko Namiki
Yasuhito Narita
Kazunari Nawa
Kiwamu Nishida
Hiroyo Ohya
Duggirala Pallamraju

Severine Rosat
Akinori Saito
Tatsuhiko Saito
David Shelly
Hisayoshi Shimizu
Wataru Suzuki
Youichiro Takada
Sunny Tam
Naoki Uchida
Yanbin Wang
Yih-Min Wu
Chuang Xuan
Takahiro Yamamoto
Yuhji Yamamoto
Tadashi Yamasaki
Yusuke Yokota
Yohei Yukutake
Seiji Zenitani

Hiroo Kanamori
Jun'ichiro Kawaguchi
Takafumi Matsui
Hitoshi Mizutani

Yasuo Ogawa
Toshitaka Tsuda
Zhongliang Wu
Kiyoshi Yomogida

Advisory Board
Benjamin Fong Chao
Bernard Chouet
Yoshimori Honkura
Toshihiko Iyemori

Journal Scope
Earth, Planets and Space (EPS) is the official journal of Society of Geomagnetism and Earth, Planetary
and Space Sciences, The Seismological Society of Japan, The Volcanological Society of Japan, The
Geodetic Society of Japan, and The Japanese Society for Planetary Sciences.
EPS is a peer-reviewed, open-access journal published under SpringerOpen. It is an international journal
covering scientific articles in the entire field of earth and planetary sciences, particularly geomagnetism,aeronomy, space science, seismology, volcanology, geodesy, and planetary science. EPS also welcomesarticles in new and interdisciplinary subjects, and technical reports on instrumentation and software.
The journal was launched in 1998 and has since published over 4000 articles. All of them are available forfree on SpringerLink:
https://link.springer.com/journal/40623/volumes-and-issues
More information about the journal, its article collections, and the submission process is available on thejournal homepage:https://earth-planets-space.springeropen.com
Submit your next research article to Earth, Planets and Space via:
https://www.editorialmanager.com/epsp
Yours sincerely,
Prof. Takeshi Sagiya
Editor-in-Chief, Earth, Planets and Space
eic@earth-planets-space.org

Earth, Planets and Space(2021) 73:56
Aoki et al. Earth, Planets and Space
https://doi.org/10.1186/s40623-021-01363-x

Open Access

PREFACEL-band Synthetic Aperture Radar: Current
and future applications to Earth sciences
Yosuke Aoki1*, Masato Furuya2, Francesco De Zan3, Marie‑Pierre Doin4, Michael Eineder3, Masato Ohki5
and Tim J. Wright6

or airborne and what we expect to learn from future
missions.
This special issue consists of 11 papers on various topics, including earthquake and volcano deformation, land
subsidence, landslide, and permafrost.
SAR images revealed that an earthquake rupture isalmost always more complicated than a shear failure ona planar fault. SAR images have demonstrated that an
earthquake rupture accompanies off-fault cracks andlineaments. Fujiwara et al. (2020) reviewed the observations of such secondary features associated with several
onshore earthquakes in the last 25 years. The geometry of
the faults on which triggered shallow slip occurs is variable; some faults are parallel to the main fault, and someare oblique or perpendicular to the main fault. However,they found some common features that tend to occur
on pre-existing weakness. Therefore, a large earthquake
in the future would also trigger shallow slips at the same
location.
Hashimoto (2020) and Ishitsuka et al. (2020) investigated the 2016 Kumamoto earthquake (Mw = 7.0).
Hashimoto (2020) investigated the first two years of postseismic deformation from ALOS-2 images. He noticed
that the L-band SAR images are coherent even if image
pairs are separated for 2 years. He also noticed that some
images are susceptible to ionospheric perturbations. The
observed deformation field is complex; the time constantof displacement decay varies between 30 to 600 days in
different locations, indicating that the observed deformation results from multiple origins. Afterslip with amixed right-lateral normal faulting mechanism explains
much of the observed deformation field, but the afterslip cannot explain observed deformation in some areas(Table 1).

Synthetic Aperture Radar (SAR) has been around formore than 40 years. The first civilian-use SAR satellite
was SeaSat, launched by National Aeronautics Space
Administration (NASA) in 1978 to monitor Earth’s
oceans. In early 1990s, we realized that SAR Interferometry (InSAR) is a powerful tool in delineating Earth’s
topography and deformation (e.g., Massonnet et al. 1993)
because SAR can image broad areas with a high spatial
resolution on the order of 10 m or less without a requirement of ground-based instruments. The advantage of
SAR as a powerful imaging tool is also because it works
day and night regardless of clouds.
SAR images taken from L-band satellites complement
satellites at shorter wavelengths such as C- and X-bands.
L-band SAR has lower resolution than C- and X-band
images but are more coherent over time, especially invegetated regions. L-band SAR data are typically easierto unwrap because of higher coherence and fewer fringes,
but more susceptible to ionospheric effects.
L-band SAR satellites for InSAR include JERS-1 (1992–
1998), ALOS (2006–2011), ALOS-2 (2014–present), andSAOCOM-1 (2017–present), which have a recurrencetime of order a few weeks. Such recurrence times do notallow monitoring with high temporal resolution. However, after the launch of ALOS-4, NISAR, and Tandem-Lin the next few years, we will be able to monitor Earth’s
surface every few days with L-band SAR. Therefore, thetime is ripe to review what we have learned from previous and ongoing L-band missions, either spaceborne*Correspondence: yaoki@eri.u‑tokyo.ac.jp
1
Earthquake Research Institute, The University of Tokyo, Tokyo, Japan
Full list of author information is available at the end of the article© The Author(s) 2021. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing,
adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) andthe source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material
in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material
is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds thepermitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativeco
mmons.org/licenses/by/4.0/.

1

L-band Synthetic Aperture Radar: Current and future applications to Earth sciences
Aoki et al. Earth, Planets and Space(2021) 73:56

Page 2 of 4

Table 1 List of SAR missions
Satellite

Band

AgencyPeriodSeasatL

US DoD

1978

ERS‑1

C

ESA

1992–1996

JERS‑1L

JAXA

1992–1998

RADARSAT‑1

C

CSA

1995–2013

ERS‑2

C

ESA

1996–2011

SRTM

C, X

NASA

2000

ENVISATC

ESA

2002–2011

ALOS

L

JAXA

2006–2011

RADARSAT‑2

C

CSA

2007–present

TerraSAR‑X

X

DLR

2007–present

COSMO‑SkyMed

X

ASI

2007–present

TanDEM‑X

X

DLR

2010–present

ALOS‑2L

JAXA

2014–present

Sentinel‑1

C

ESA

2014–present

SAOCOML

CONAE/ASI

2017–present

NISAR

L

NASA/ISRO

2021 (planned)

ALOS‑4L

JAXA

2022 (planned)

Tandem‑L

L

DLR(planned)

InSAR is a powerful tool to investigate moderate-sized(M < 6.5) earthquakes when local and regional seismic
data are not available. Ghayournajarkar and Fukushima(2020) demonstrated another example with the 2017
Sefid Sang, northern Iran, earthquake (Mw = 6.1) from
ALOS-2 and Sentinel-1 images. The observed displacement field fits well with both northeast- and southwest-dipping faults, but the aftershock distribution andorientation of active faults led them to conclude thatthe northeast-dipping fault is more favorable than thesouthwest-dipping fault. Their study demonstrates theutility of SAR images to investigate middle-sized earthquakes. Simultaneously, it demonstrates the difficulty inconstraining which of two conjugate planes is responsible
for the earthquake even with interferograms from bothascending and descending images.
Wang et al. (2019) and Narita et al. (2020) investigatedvolcano deformation. Wang et al. (2019) measured surface deformation near the vent of Asama Volcano, Japan,
during its relatively dormant period (2014–2018). They
employed not only ALOS-2 but also Sentinel-1 images
to take advantage of more frequent acquisitions. Theirtime series analysis revealed surface deformation of up to
7 mm/year to the northeast and southeast of the summit.
The surface deformation to the southeast of the summit is likely due to flank sliding, while the origin of thatto the northeast of the summit is ambiguous. Although
the area coincides with the lava deposit by a previous
large eruption, thermal contraction is not responsible forthis observed deformation because a theoretical consideration indicates the observed thermal contraction there
should be negligible by now. The origin of the deformation there is either by flank sliding or due to hydrothermal activity. Flank sliding to the northeast of the summit
should be northward, but the insensitivity to north–south
displacements of spaceborne InSAR prevents the authors
from confirming that the observed displacements there
are due to flank sliding.
Narita et al. (2020) measured surface deformation
between 2014 and 2018 from ALOS-2 and airborne PiSAR-L2 images. Utilizing airborne SAR images takes
advantage of delineating arbitrary components of displacements, while interferograms from spaceborne
SAR images are insensitive to north–south displacements because of the polar orbit of the satellite. The
observed three-dimensional displacement field and its
temporal evolution led Narita et al. (2020) to postulate
two hydrothermal reservoirs at ~ 150 and ~ 700 m below
sea level, with an impermeable bed between them. Theyinterpreted that accelerating flux of hydrothermal fluid
from depth to the deeper reservoir led to accelerating
flux of hydrothermal fluid from the deeper to shallower
reservoir. They concluded that the pressurization of

Ishitsuka et al. (2020) also investigated the postseismic
deformation of the Kumamoto earthquakes, as Hashimoto (2020) did. They processed Sentinel-1 and ALOS-2
images to gain temporal resolution and detected deformation associated with groundwater movement. Theyinterpreted postseismic subsidence which correlates withpostseismic groundwater drawdown. They also detectedseasonal deformation, which correlates with the seasonalvariation of water level. The amplitude of seasonal deformation increased after the Kumamoto earthquake. Thesefindings suggest that the Kumamoto earthquake changed
aquifer permeability, compressibility, or both, leading
to enhanced deformation associated with groundwater
movement.
Fukushima et al. (2019) investigated another onshore
earthquake, the 2017 Ormoc (Mw = 6.5), on the creeping
Philippine fault in Leyte island, the Philippines. They processed ALOS and ALOS-2 images to find that the Philippine fault is creeping with a rate of 33 ±11 mm/year in
the northern and central part of the Leyte island except
for the locked portion where the Ormoc earthquake took
place. An investigation of teleseismic records of the 1947
earthquake (Ms = 6.9) revealed that the Ormoc earthquake and the 1947 earthquake exhibit the repeating rupture within the same locked patch. They also inferred thatthe 1947 earthquake of Ms = 6.9 is nearly the maximum
earthquake the Philippine fault can generate in the northern and central Leyte island. Their study demonstrates
the utility of SAR images to assess large earthquakes
along creeping faults.

2Earth, Planets and Space
Aoki et al. Earth, Planets and Space(2021) 73:56

Page 3 of 4

that land subsidence would pose 635 million people atrisk by 2040. SAR is a powerful tool to detect and monitor land subsidence because of its high spatial resolution.
Li et al. (2020) found from ALOS images that more than
122 km2 of the Pearl River Delta, southern China, subsided by more than 30 mm/year between 2006 and 2011.
In particular, the front part of the delta and the coastal
area were subsiding by more than 50 mm/year. Theseobservations led Li et al. (2020) to interpret that the subsidence is partly due to the thick, soft soil layer and partly
due to human interference, such as reclamation, groundwater extraction, and urban construction.
This special issue demonstrates the utility of SAR
images, L-band SAR images in particular, for various
Earth Science applications including, but not limited
to, earthquake and volcano deformation, landslide, glaciology, and land subsidence. In the next few years, thelaunch of new L-band satellites, including ALOS-4,
NISAR, and Tandem-L, will give us a powerful new toolwith which to make exciting discoveries, in particular bycombining these L-band images with pre-existing C- andX-band SAR images.

the shallower reservoir triggered a phreatic eruption in
April 2018.
Various origins, including earthquake shaking andheavy rainfall, trigger landslides. SAR is a useful tool todetect and monitor landslides because of its high spatial resolution. Takada and Motono (2020) investigateddetails of a large landslide site at Mt. Onnebetsu-dake,northeastern Japan, in the last ~ 25 years from JERS1, ALOS, and ALOS-2 images. The landslide velocity changes over time with a maximum of 60 mm/
year of eastward velocity and ~ 20 mm/year of subsidence between 2014 and 2017. They interpreted that
this velocity increase is due to increased pore pressure resulting from elevated annual rainfall duringthat period. They also found a shorter-term increaseof landslide velocity in August 2016, by heavy rainfall.
These observations indicate that both long- and shortterm variations of rainfall affect the dynamics of landslides. The internal deformation within the landslidesite indicates that the gravitational forces primarily
drive the landslide.
While Takada and Motono (2020) focused on the
dynamics of landslides, Ohki et al. (2020) focused on
detecting landslides. They combined SAR polarimetry(PolSAR), InSAR, and Digital Elevation Model (DEM), todevelop an algorithm to detect landslides. They applied
their method to landslides by the 2017 heavy rainfall innorthern Kyushu, Japan, and the 2018 Hokkaido Eastern
Iburi, Japan, earthquake to find that polarimetric parameters, e.g., the alpha angle and Pauli components, aregood indicators to discriminate damaged areas. They also
found that supervised classification with PolSAR, InSAR,
and DEM works well, although the classification accuracy
depends on the training data’s geological characteristics.
These findings demonstrate the utility of SAR images todetect landslides quickly.
Recent global warming causes ground deformation
due to excess melting of ground ice, and the processes
to form subsequent terrain are called thermokarst. Abe
et al. (2020) mapped subsidence due to thermokarst inCentral Yakutia, Russia, with ALOS and ALOS-2 images.
They detected a subsidence of 5–30 mm/year with seasonal variation in deforested areas, while the deformation
in forested regions is negligible. This difference is consistent with the thermokarst dynamics through freezing andthawing. Also, the observation from the SAR images is
consistent with field measurements and optical images.
They found that L-band SAR images are useful in longterm monitoring permafrost areas because of persistentcoherence.
Land subsidence of natural and anthropogenic origin, as well as global warming, is an issue that threatens
human life. Herrera-García et al. (2021) recently reported

Abbreviations
ALOS: Advanced Land Observing Satellite; ASI: Agenzia Spaziale Italiana(Italian Space Agency); CONAE: Comisión Nacional de Actividades Espaciales(National Space Activities Commission of Argentina); COSMO‑SkyMed:
Constellation of Small Satellites or Mediterraneanbasin Observation; CSA:
Canadian Space Agency; DLR: Deutsches Zentrum für Luft‑ und Raumfahrt(German Aerospace Center); ENVISAT: Environmental Satellite; ERS: European
Remote‑Sensing Satellite; ESA: European Space Agency; InSAR: Synthetic
Aperture Radar Interferometry; ISRO: Indian Space Research Organization;
JAXA: Japan Aerospace Exploration Agency; NASA: National Aeronautics
Space Administration; SAR: Synthetic Aperture Radar; TanDEM‑X: TerraSAR
add‑on for Digital Elevation Measurement; US DoD: United States Departmentof Defense.
Acknowledgements
We thank authors and reviewers who contributed to organize this special
issue. We also thank Editor‑in‑Chief Yasuo Ogawa for recommending to organ‑
ize this special issue.
Authors’ contribution
All authors served as guest editors for this special issue, YA being the lead
guest editor. All authors read and approved the final manuscript.
Ethical approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Competing interests
The authors declare that they have no competing interests.
Author details
1
Earthquake Research Institute, The University of Tokyo, Tokyo, Japan.
2
Department of Natural History Science, Hokkaido University, Sapporo,
Japan. 3 Remote Sensing Technology Department, German Aerospace Center,
Weßling, Germany. 4 Institut Des Sciences de La Terre, Université Grenoble
Alpes, Grenoble, France. 5 Japan Aerospace Exploration Agency, Chofu, Japan.
6
COMET, School of Earth and Environment, University of Leeds, Leeds, UK.

3

L-band Synthetic Aperture Radar: Current and future applications to Earth sciences
Aoki et al. Earth, Planets and Space(2021) 73:56

Page 4 of 4

Received: 15 January 2021 Accepted: 15 January 2021

2016 Kumamoto earthquake: implications for seismic‑induced ground‑water level change. Earth Planets Space 72:144. https://doi.org/10.1186/
s40623‑020‑01275‑2
Li G, Feng G, Xiong Z, Liu Q, Xie R, Zhu X, Luo S, Du Y (2020) Surface deforma‑tion evolution in the Pearl River Delta between 2006 and 2011 derived
from the ALOS1/PALSAR images. Earth Planets Space 72:179. https://doi.
org/10.1186/s40623‑020‑01310‑2
Massoneet D, Rossi M, Camona C, Adragna F, Peltzer G, Feigl K, Rabaute T(1993) The displacement field of the Landers earthquake mapped byradar interferometry. Nature 364:138–142. https://doi.org/10.1038/36413
8a0
Narita S, Ozawa T, Aoki Y, Shimada M, Furuya M, Takada Y, Murakami M (2020)
Precursory ground deformation of the 2018 phreatic eruption on Iwo‑
Yama volcano, revealed by four‑dimensional joint analysis of airborne andspaceborne InSAR. Earth Planets Space 72:145. https://doi.org/10.1186/
s40623‑020‑01280‑5
Ohki M, Abe T, Tadono T, Shimada M (2020) Landslide detection in mountain‑
ous forest areas using polarimetry and interferometric coherence. Earth
Planets Space 72:67. https://doi.org/10.1186/s40623‑020‑01191‑5
Takada Y, Motono G (2020) Spatiotemporal behavior of a large‑scale landslideof Mt Onnebetsu‑dake, Japan, detected by three L‑band SAR satellites.
Earth Planets Space 72:1331. https://doi.org/10.1186/s40623‑020‑01265‑4
Wang X, Aoki Y, Chen J (2019) Surface deformation of Asama Volcano, Japan,
detected by time series InSAR combining persistent distributed scat‑terers, 2014–2018. Earth Planets Space 71:121. https://doi.org/10.1186/
s40623‑019‑1104‑9References
Abe T, Iwahana G, Efremov PV, Desyatkin AR, Kawamura T, Fedorov A,
Zhegusov Y, Yanagiya K, Tadono T (2020) Surface displacement revealedby L‑band InSAR analysis in the Mayya area, Central Yakutia, underlain
by continuous permafrost. Earth Planets Space 72:138. https://doi.
org/10.1186/s40623‑020‑01266‑3
Fukushima Y, Hashimoto M, Miyazawa M, Uchida N, Taira T (2019) Surface
creep rate distribution along the Philippine fault, Leyte Island, and pos‑sible repeating of Mw~65 earthquakes on an isolated locked patch. Earth
Planets Space 71:118. https://doi.org/10.1186/s40623‑019‑1096‑5
Fujiwara S, Nakano T, Morishita Y (2020) Detection of triggered shallow slips
caused by large earthquakes using L‑band SAR interferometry. Earth
Planets Space 72:119. https://doi.org/10.1186/s40623‑020‑01239‑6
Ghayournajarkar N, Fukushima Y (2020) Determination of the dipping direc‑
tion of a blind reverse fault from InSAR: case study on the 2017 Sefid
Sang earthquake, northeastern Iran. Earth Planets Space 72:64. https://doi.org/10.1186/s40623‑020‑01190‑6
Hashimoto M (2020) Postseismic deformation following the 2016 Kumamoto
earthquake detected by ALOS‑2/PALSAR‑2. Earth Planets Space 72:154.
https://doi.org/10.1186/s40623‑020‑01285‑0
Herrera‑García G, Ezquerro P, Tomás R, Béjar‑Pizarro M, López‑Vinielles J, Rossi
M, Mateos RM, Carreón‑Freyre D, Lambert J, Teatini P, Cabrai‑Cano E,
Erkens G, Galloway D, Hung W‑C, Kakar N, Sneed M, Tosi L, Wang H, Ye S
(2021) Mapping the global threat of land subsidence. Science 371:34–36.
https://doi.org/10.1126/science.abb8549
Ishitsuka K, Tsuji T, Lin W, Kagabu M, Shimada J (2020) Seasonal and transient
surface displacements in the Kumamoto area, Japan, associated with the

Publisher’s NoteSpringer Nature remains neutral with regard to jurisdictional claims in pub‑lished maps and institutional affiliations.

4Earth, Planets and SpaceFRONTIER LETTER

Open Access

Detection of triggered shallow slips caused by large
earthquakes using L-band SAR interferometry
Satoshi Fujiwara*, Takayuki Nakano and Yu Morishita
Earth, Planets and Space 2020, 72:119 DOI: 10.1186/s40623-020-01239-6
Received: 14 February 2020, Accepted: 22 July 2020, Published: 13 August 2020

Abstract
Interferograms pertaining to large earthquakes typically reveal the occurrence of elastic deformations caused by the earthquake alongwith several complex surface displacements. In this study, we identified displacement lineaments from interferograms; some of which
occur on the shallow section of seismogenic faults. However, such displacements are typically located away from the hypocenter, andthey are considered as triggered shallow slips. We found that the triggered shallow slips had a varied nature, as follows. (1) No evidence
has yet been obtained regarding the generation of large seismic motion via triggered shallow slips; thus, their occurrence is seldom
considered a cause of major earthquakes. However, we found that a movement of triggered shallow slip associated with an M6-class
earthquake occurred on an active fault that has previously caused an M7-class earthquake. (2) At certain locations, several parallel
displacement lineaments have been discovered. During the Kumamoto earthquake sequence in 2016, the strain created by the main
shock and the motion of triggered shallow slips coincided at a specific location, resulting in the creation of parallel triggered shallow
slips by the main shock. Conversely, at another location, the movements of the main shock and triggered shallow slips did not match,since the main shock was simply a trigger, whereas the latter parallel triggered shallow slips are likely a means for releasing previously
accumulated strain. (3) The fault scaling law—which states that the length and displacement of a fault are proportional—does not holdtrue for triggered shallow slips. However, the parallel triggered shallow slips show a
Vertical displacement cross sections
2016 Kumamoto
relationship between horizontal spacing and its displacement. This may be attributed
Bearthquake sequenceAto immobility in deep locations. These results lead to the following conclusions. Large
Aearthquakes tend to trigger shallow slips on the pre-existing faults. Subsequently,
these triggered shallow slips release accumulated strain by causing fault motions,B
which in turn result in displacement lineaments. The occurrence of such passive
CCD
faulting creates weak, mobile fault planes that repeatedly move at the same location.
These triggered shallow slips cause the diversity among active faults as a result.
1000

10

900

Topo (m)Up--Down (cm)

20

0

800

-10
-20

0

1

2

3

4 km

Keywords: L-band SAR interferometry, JERS-1, ALOS, ALOS-2, Earthquake,
Displacement lineament, Triggered shallow slip

10

700

800
700

Topo (m)Up--Down (cm)

20

0

600

-10
-20

0

1

2

3

4 km

500

D

South side
Down

Up

Graphical abstract*Corresponding author: Satoshi Fujiwara, fujiwara-s2vq@mlit.go.jp

FULL PAPER

Open Access

Surface creep rate distribution along the Philippine fault, Leyte Island,and possible repeating of Mw ~ 6.5 earthquakes on an
isolated locked patch
Yo Fukushima*, Manabu Hashimoto, Masatoshi Miyazawa, Naoki Uchida and Taka’aki Taira
Earth, Planets and Space 2019, 71:118 DOI: 10.1186/s40623-019-1096-5
Received: 1 May 2019, Accepted: 23 October 2019, Published: 9 November 2019

Abstract
Active faults commonly repeat cycles of sudden rupture and subsequent silence of hundreds to tens of thousands of years, but someparts of mature faults exhibit continuous creep accompanied by many small earthquakes. Discovery and detailed examination of
creeping faults on land have been in a rapid progress with the advent of space-borne synthetic aperture radar interferometry. In thisstudy, we measured the spatial variation of the creep rate along the Philippine fault on Leyte Island using ALOS/PALSAR data acquired
between October 2006 and January 2011. Prominent creep of 33±11 mm/year was estimated in northern and central parts of the island
except for a locked portion around latitude 11.08–11.20°N. We
compared the creep rate distribution along the fault with the slip
distribution of the 2017 Mw 6.5 Ormoc earthquake which occurred innorthern Leyte, estimated from the displacements mapped by ALOS-2/
PALSAR-2 interferometric data. The estimated slip of the 2017
earthquake amounted up to 2.5 m and to moment magnitude of 6.49,
with the dominant rupture area coinciding with the locked portion
identified from the interseismic coupling analysis. Teleseismic
waveforms of the 2017 earthquake and another event that occurred in1947 (Ms 6.9) exhibit close resemblance, indicating two ruptures ofrather similar locations and magnitudes with a time interval of 70 years.

Keywords: Philippine fault, Leyte Island, Crustal deformation, SAR

interferometry, InSAR, Fault creep, Repeating earthquake,
Characteristic earthquake, Historical seismograms*Corresponding author: Yo Fukushima, fukushima@irides.tohoku.ac.jp
5Graphical abstract

L-band Synthetic Aperture Radar: Current and future applications to Earth sciences

FULL PAPER

Open Access

Surface deformation of Asama volcano, Japan, detected bytime series InSAR combining persistent and distributed
scatterers, 2014–2018
Xiaowen Wang*, Yosuke Aoki and Jie Chen
Earth, Planets and Space 2019, 71:121 DOI: 10.1186/s40623-019-1104-9
Received: 22 July 2019, Accepted: 1 November 2019, Published: 14 November 2019

Abstract
Asama volcano is one of the most active volcanoes in Japan. Spatially dense surface deformation at Asama volcano has rarely been documented
because of its high topography and snow cover around the summit. This study presents the first interferometric synthetic aperture radar (InSAR)
observation of ground deformation at Asama volcano with 120 Sentinel-1 SAR images from both ascending and descending tracks and 20
descending ALOS-2 images acquired between 2014 and 2018. We exploited both persistent and distributed scatterers to overcome decorrelationof SAR signals and applied a three-dimensional unwrapping method to retrieve the displacement time series efficiently. Our observations reveal
an asymmetric deformation around the volcano with two main deformation regions on the northeast and southeast flanks, respectively. The
northeast flank (NEF) exhibits line-of-sight (LOS) extensions in all the three SAR datasets with maximum velocities of − 14, − 10, and − 12 mm/year
for the descending ALOS-2, ascending, and descending Sentinel-1 measurements, respectively. The southeast flank (SEF) shows LOS extensions in
the ascending observations and LOS shortening in the descending observations with velocities between − 12 and 9 mm/year. Decomposition of
the LOS displacements reveals nearly pure subsidence at the NEF, while the SEF exhibits a substantial eastward component as well as subsidence.
Comparisons of the vertical subsidence at two continuous GNSS stations near
the summit crater with our InSAR observations indicate small discrepancies
smaller than 4 mm/year. We interpreted that the subsidence at the NEF of
Asama is primarily due to the hydrothermal activity, while the deformation at
SEF is plausibly due to flank instability. We highlight that efforts should betaken to monitor the slope instability at Asama volcano in the future.

Keywords: Asama volcano, InSAR, Volcano deformation, Persistent
scatterers, Distributed scatterers, Slope instability

Graphical abstract*Corresponding author: Xiaowen Wang, insarwxw@gmail.com

FULL PAPER

Open Access

Determination of the dipping direction of a blind reverse fault
from InSAR: case study on the 2017 Sefid Sang earthquake,
northeastern Iran
Nematollah Ghayournajarkar* and Yo Fukushima
Earth, Planets and Space 2020, 72:64 DOI: 10.1186/s40623-020-01190-6
Received: 22 January 2020, Accepted: 28 April 2020, Published: 12 May 2020

Abstract
Determining the fault parameters of an earthquake is fundamental for studying the earthquake physics, understanding the seismotectonics ofthe region, and forecasting future earthquake activities in the surrounding area. Dense crustal deformation data such as Interferometric Synthetic
Aperture Radar (InSAR) are useful for fault parameter determination, but determining the dipping direction of a blind fault is often challenging
when the size of the earthquake is not large (M < 7) or when the coverage of the deformed area is limited to capture the details of rupture. The 5th
April 2017, Mw 6.1 earthquake occurred near the city of Sefid Sang, northeast of Iran, provides an excellent
case for exploring the potential of InSAR data for determining the dipping direction of a blind reverse fault.
Using Advanced Land Observing Satellite-2 (ALOS-2) and Sentinel-1A interferograms of four different
observation directions and a fault slip inversion method that allows thorough exploration of the fault
geometry led to two candidates of reverse fault models, dipping either to the northeast or the south. The
results show that the fault models of both dipping directions explain the data well, with a slight advantage in
the northeast-dipping fault model in terms of the misfit when the atmospheric corrections were applied. The
northeast-dipping fault model is, in addition, more consistent with the strike of the mapped active faults in
the region and with the aftershock distribution, from which we infer that the 2017 Sefid Sang earthquake
occurred on a northeast-dipping dextral-reverse fault. The preferred fault model has a strike angle of 314.8°,
dip angle of 47.4° and rake angle of 130.3°, and a slip distribution of maximum 1.35 m at depth of 5 km
equivalent to Mw 6.0. This study illuminates the difficulty of determining the dipping direction of blind faults
even with InSAR measurements from multiple directions, but also that correcting for the atmospheric noiseand comparing with other kinds of data can help infer the fault dipping direction.

Keywords: InSAR, Sefid Sang earthquake, Blind reverse fault, Coseismic deformation, Northeastern Iran,
ALOS-2, Sentinel-1AGraphical abstract*Corresponding author: Nematollah Ghayournajarkar, nghayour@dc.tohoku.ac.jp
6Earth, Planets and Space

FULL PAPER

Open Access

Landslide detection in mountainous forest areas using
polarimetry and interferometric coherence
Masato Ohki*, Takahiro Abe, Takeo Tadono and Masanobu Shimada
Earth, Planets and Space 2020, 72:67 DOI: 10.1186/s40623-020-01191-5
Received: 16 January 2020, Accepted: 4 May 2020, Published: 13 May 2020

Abstract
The cloud-free, wide-swath, day-and-night observation capability of synthetic aperture radar (SAR) has an important role in rapid
landslide monitoring to reduce economic and human losses. Although interferometric SAR (InSAR) analysis is widely used to monitor
landslides, it is difficult to use that for rapid landslide detection in mountainous forest areas because of significant decorrelation. We
combined polarimetric SAR (PolSAR), InSAR, and digital elevation model (DEM) analysis to detect landslides induced by the July 2017
Heavy Rain in Northern Kyushu and by the 2018 Hokkaido Eastern Iburi Earthquake. This study uses fully polarimetric L-band SAR datafrom the ALOS-2 PALSAR-2 satellite. The simple thresholding of polarimetric parameters (alpha angle and Pauli components) was foundto be effective. The study also found that supervised classification using PolSAR, InSAR, and DEM parameters provided high accuracy,
although this method should be used carefully because its accuracy depends on the geological characteristics of the training data.
Regarding polarimetric configurations, at least
dual-polarimetry (e.g., HH and HV) is required forlandslide detection, and quad-polarimetry is
recommended. These results demonstrate thefeasibility of rapid landslide detection using L-band
SAR images.

Keywords: Synthetic aperture radar (SAR),

ALOS-2, Disaster monitoring, 2018
Hokkaido Eastern Iburi Earthquake,
July 2017 Heavy Rain in Northern
Kyushu, Machine learning
Graphical abstract*Corresponding author: Masato Ohki, ohki.masato@jaxa.jp

FULL PAPER

Open Access

Spatiotemporal behavior of a large-scale landslide at
Mt. Onnebetsu-dake, Japan, detected by three L-band SAR
satellites
Youichiro Takada* and George Motono
Earth, Planets and Space 2020, 72:131 DOI: 10.1186/s40623-020-01265-4
Received: 8 April 2020, Accepted: 2 September 2020, Published, 11 September 2020

Abstract
We applied differential InSAR analysis to the Shiretoko Peninsula, northeastern Hokkaido, Japan. All the interferograms of long temporal baseline(~ 3 years) processed from SAR data of three L-band satellites (JERS-1, ALOS, ALOS-2) commonly indicate remarkable phase changes due to thelandslide movement at the southeastern flank of Mt. Onnebetsu-dake, a Quaternary stratovolcano. The area of interferometric phase change
matches to known landslide morphologies. Judging from the timing of the SAR image acquisitions, this landslide has been moving at least from1993 to the present. Successive interferograms of 1-year temporal baseline indicate the temporal fluctuation of the landslide velocity. Especiallyfor the descending interferograms, the positive line-of-sight (LOS) length change, which indicates large subsidence relative to the horizontal
movement, is observed in the upslope section of the landslide during 1993–1998, while the negative LOS change is observed in the middle andthe downslope section after 2007 indicating less subsidence. The landslide activity culminates from 2014 to 2017: the eastward and the verticaldisplacement rates reach ~ 6 and ~ 2 cm/yr, respectively. Utilizing high spatial resolution of ALOS and ALOS-2 data, we investigated velocity
distribution inside the landslide. During 2007–2010, the eastward component of surface displacement increases toward the east, implying thatthe landslide extends toward the east. During 2014–2017, the verticaldisplacement profile exhibits spatially periodic uplift and subsidence consistent
with surface gradient, which indicates the ongoing deformation driven by
gravitational force. Heavy rainfall associated with three typhoons in August 2016
might have brought about an increase in the landslide velocity, possibly due toelevated pore-fluid pressure within and/or at the base of the landslide material.
Also, annual rainfall would be an important factor that prescribes the landslide
velocity averaged over 3 years.

Keywords: Slow-moving landslide, L-band, InSAR, JERS-1, ALOS, ALOS-2,
Hokkaido

Graphical abstract*Corresponding author: Youichiro Takada, takaday@sci.hokudai.ac.jp
7L-band Synthetic Aperture Radar: Current and future applications to Earth sciences

FULL PAPER

Open Access

Surface displacement revealed by L-band InSAR analysis
in the Mayya area, Central Yakutia, underlain by continuous
permafrost
Takahiro Abe*, Go Iwahana, Petr V. Efremov, Alexey R. Desyatkin, Takumi Kawamura,
Alexander Fedorov, Yuri Zhegusov, Kazuki Yanagiya and Takeo Tadono
Earth, Planets and Space 2020, 72:138 DOI: 10.1186/s40623-020-01266-3
Received: 22 March 2020, Accepted: 4 September 2020, Published: 22 September 2020

Abstract
Recent increases in global temperature have stimulated permafrost degradation associated with landform deformation caused by the melting ofexcess ground ice (thermokarst). Central Yakutia is underlain by ice-rich continuous permafrost, and there are complicated permafrost-related
features in forested and deforested areas. This situation makes thermokarst monitoring necessary over a wide area to achieve a better
understanding of its dynamics. As a case study, we applied L-band InSAR analysis to map surface subsidence due to thermokarst in this area andto demonstrate the suitability of L-band SAR for such monitoring. Our results show that InSAR detected subsidence/uplift signals in deforested
areas and alasses; whereas, there were few ground deformation signals in forested areas with middle coherence. The InSAR stacking process,including both seasonal and inter-annual displacements, showed subsidence in deforested areas during 2007–2010 and 2015–2018, in the rangeof 0.5–3 cm yr−1. We also estimated the inter-annual subsidence to be up to 2 cm yr−1 during 2015–2018, using InSAR pairs that spanned the same
seasonal interval but in different years. The magnitude of subsidence and the spatial patterns are qualitatively reasonable as thermokarst
subsidence compared to observations using field surveys andhigh-resolution optical images. L-band InSAR was effective inmaintaining coherence over a long period for a partially forested
thermokarst-affected area, which resulted in deriving the inter-annual
subsidence by the stacking using four interferograms. The advantageof the persistent coherence in L-band InSAR is crucial to better
understand thermokarst processes in permafrost regions.

Keywords: Permafrost, Thermokarst, Central Yakutia, Siberia,
InSAR, Stacking, L-band, ALOS, ALOS-2

Graphical abstract*Corresponding author: Takahiro Abe, abe.takahiro2@jaxa.jp

FULL PAPER

Open AccessSeasonal and transient surface displacements in the Kumamoto area,
Japan, associated with the 2016 Kumamoto earthquake:
implications for seismic-induced groundwater level change
Kazuya Ishitsuka*, Takeshi Tsuji, Weiren Lin, Makoto Kagabu and Jun Shimada
Earth, Planets and Space 2020, 72:144 DOI: 10.1186/s40623-020-01275-2
Received: 29 December 2019, Accepted: 17 September 2020, Published: 9 October 2020

Abstract
The 2016 Kumamoto earthquake sequence on April 14 (Mw 6.2) and April 16 (Mw 7.0) altered the regional groundwater level. To better understandthe relationship between groundwater level change and surface displacement, we estimated surface displacement in the Kumamoto area
(Japan) using persistent scatterer interferometry from 19 ALOS/PALSAR images acquired between January 7, 2007 and March 5, 2011, 28 ALOS-2/
PALSAR-2 images acquired between April 17, 2016 andDecember 10, 2018, and 113 Sentinel-1 images acquired
between May 26, 2016 and December 30, 2018. Our estimationshows that transient surface displacement occurred following
the 2016 Kumamoto earthquake sequence, together withseasonal surface displacement that was not detected from the
2007–2011 images. We suggest that a portion of the transient
displacement occurred via groundwater drawdown throughnew ruptures that formed owing to the 2016 Kumamoto
earthquake sequence and sediment compaction. Seasonal
surface displacements detected after the 2016 Kumamoto
earthquake sequence are linked to groundwater level variations.

Keywords: Post-seismic displacement, Groundwater,

Persistent scatterer interferometry, The 2016
Kumamoto earthquake sequence, PALSAR-2,
PALSAR, Sentinel-1

Graphical abstract*Corresponding author: Kazuya Ishitsuka, ishitsuka.kazuya.4w@kyoto-u.ac.jp
8Earth, Planets and Space

FULL PAPER

Open AccessPrecursory ground deformation of the 2018 phreatic eruption on
Iwo-Yama volcano, revealed by four-dimensional joint analysis
of airborne and spaceborne InSAR
Shohei Narita*, Taku Ozawa, Yosuke Aoki, Masanobu Shimada, Masato Furuya, Youichiro Takada
and Makoto Murakami
Earth, Planets and Space 2020, 72:145 DOI: 10.1186/s40623-020-01280-5
Received: 8 April 2020, Accepted: 23 September 2020, Published: 9 October 2020

Abstract
We present detailed maps of local-scale 3D deformation preceding the 2018 phreatic eruption at Iwo-yama volcano (south of Kyushu Island,
Japan), using a combination of airborne and spaceborne Interferometric Synthetic Aperture Radar (InSAR) data. The 3D and 2.5D deformation
maps obtained at different periods allow us to successfully track their spatiotemporal evolution and to infer the transition of subsurface
conditions responsible for the precursory deformation observed from 2014 to 2018. From 2014 to 2016, ground inflation depicted anaxisymmetric pattern with the maximum displacement at the center of the deformed area. However, from 2016 to
2018, an inflation peak moved to the southern edge of the area deformed during 2014–2016 and became more
localized, which was close to the newly generated vents in the 2018 eruption. Modeling of the inflations suggeststhat pressurization within a crack at a depth of 150 m beneath the Iwo-yama geothermal area caused the 2014–2016 deformation and had continued until the 2018 eruption. Modeling results highlight the persistence of thelocal ground inflation pattern just above the southern edge of the crack, which suggests the presence of ashallower inflation source contributing to the local inflation. Consequently, we interpret the sequence of thesedeformations as follows: from 2014, deeper-rooted fluid started to inject into a fluid-saturated crack at 150-m
depth, which caused the 2014–2016 deformation. Then, after 2016, the crack inflation continued because of thecontinuous fluid injection and formed another pressurized part directly above the southern tip of the crack.
Additionally, the results of the time-series analysis of the satellite InSAR data revealed that the local inflation started
around April 2017 for which thermal activity including a mud emission became pronounced around the location of
the local inflation. As a result of an episodic increase in supply rate of magmatic fluids from a deep magma reservoir
from early 2018, a phreatic eruption finally occurred in the vicinity of the most deformed point, providing a clue forpredicting future eruption sites, as was also observed in the Hakone 2015 eruption.

Keywords: InSAR, Phreatic eruption, Ground inflation, Volcanic hydrothermal system, Airborne SAR, Iwo-yamaGraphical abstract*Corresponding author: Shohei Narita, narita.shohei.6n@kyoto-u.ac.jp

FULL PAPER

Open Access

Postseismic deformation following the 2016 Kumamoto
earthquake detected by ALOS-2/PALSAR-2
Manabu Hashimoto
Earth, Planets and Space 2020, 72:154 DOI: 10.1186/s40623-020-01285-0
Received: 31 March 2020, Accepted: 30 September 2020, Published: 20 October 2020

Abstract
I have been conducting a study of postseismic deformation following the 2016 Kumamoto earthquake using ALOS-2/PALSAR-2 acquired
till 2018. I apply ionospheric correction to interferograms of ALOS-2/PALSAR-2. L-band SAR gives us high coherence enough to reveal
surface deformation even in vegetated or mountainous area for pairs of images acquired more than 2 years. Postseismic deformation
following the Kumamoto earthquake exceeds 10 cm during 2 years at some spots in and around Kumamoto city and Aso caldera.
Westward motion of ~ 6 cm/year was dominant on the southeast side of the Hinagu fault, while westward shift was detected on bothsides of the Futagawa fault. The area of latter deformation seems to have correlation with
distribution of pyroclastic flow deposits. Significant uplift was found around the eastern Futagawa
fault and on the southwestern frank of Aso caldera, whose rate reaches 4 cm/year. There are sharpchanges across several coseismic surface ruptures such as Futagawa, Hinagu, and Idenokuchi faults.
Rapid subsidence between Futagawa and Idenokuchi faults also found. It is confirmed that local
subsidence continued along the Suizenji fault, which newly appeared during the mainshock in
Kumamoto City. Subsidence with westward shift of up to 4 cm/year was also found in Aso caldera.
Time constant of postseismic decay ranges from 1 month to 600 days at selected points, but thatpostseismic deformation during the first epochs or two is dominant at point in the Kumamoto Plain.
This result suggests multiple source of deformation. Westward motion around the Hinagu fault may
be explained with right lateral afterslip on the shallow part of this fault. Subsidence along the
Suizenji fault can be attributed to normal faulting on dipping westward. Deformation around theHinagu and Idenokuchi faults cannot be explained with right lateral afterslip of Futagawa fault,
which requires other sources. Deformation in northern part of Aso caldera might be the result ofright lateral afterslip on a possible buried fault.

Keywords: Kumamoto earthquake, Postseismic deformation, ALOS-2/PALSAR-2, Ionosphericcorrection, InSAR

Corresponding author: Manabu Hashimoto, hashimoto.manabu.7e@kyoto-u.ac.jp
9Graphical abstract

L-band Synthetic Aperture Radar: Current and future applications to Earth sciences

FULL PAPER

Open Access

Surface deformation evolution in the Pearl River Delta
between 2006 and 2011 derived from the ALOS1/PALSAR
imagesGenger Li, Guangcai Feng*, Zhiqiang Xiong, Qi Liu, Rongan Xie, Xiaoling Zhu,
Shuran Luo and Yanan Du
Earth, Planets and Space 2020, 72:179 DOI: 10.1186/s40623-020-01310-2
Received: 27 May 2020, Accepted: 9 November 2020, Published: 26 November 2020

Abstract
This study monitors the land subsidence of the whole Pearl River Delta (PRD) (area: ~ 40,000 km2) in China using the ALOS1/PALSAR data (2006–2011) through the SBAS-InSAR method. We also analyze the relationship between the subsidence and thecoastline change, river distribution, geological structure as well as the local terrain. The results show that (1) the land subsidencewith the average velocity of 50 mm/year occurred in the low elevation area in the front part of the delta and the coastal area, andthe area of the regions subsiding faster than 30 mm/year
between 2006 and 2011 is larger than 122 km2; (2) the
subsidence order and area estimated in this study are bothmuch larger than that measured in previous studies; (3) the
areas along rivers suffered from surface subsidence, due tothe thick soft soil layer and frequent human interference; (4)the geological evolution is the intrinsic factor of the surface
subsidence in the PRD, but human interference (reclamation,
ground water extraction and urban construction) extends thesubsiding area and increases the subsiding rate.

Keywords: Pearl river delta, Natural evolution, Surface
subsidence, SBAS-InSAR

Graphical abstract*Corresponding author: Guangcai Feng, fredgps@qq.com

10

Information for Contributors
General1.

Manuscripts should be submitted through the journal’s Editorial Manager system(https://www.editorialmanager.com/epsp/default.aspx).

2.

Only papers not previously published will be accepted, and the emphasis is on theoriginality of concept or observation.

3.

Five varieties of article types are available.
3.1“Full Paper” without word limit.

3.2“Express Letter” has a limit of 5000 words including the main text, figure legends
and table legends. The sum of the number of figures and tables should be lessthan or equal to 5.

3.3“Frontier Letter” can be submitted upon invitation by the Editor-in-Chief.

3.4“Technical Report” describes the technical development of instrument or software.

3.5“Comment” is a substantial re-analysis of a previously published article in thejournal. ”Comment” should not exceed 1000 words.

4.

Authors retain the copyright, and distribution of articles is free under the CC BY license.

Technical
1.

Manuscripts should be written in English with double spacing.

2.

Each manuscript should be organized in the following order: title, authors’ names,
affiliations, abstract, key words, main text, acknowledgement, appendix, references, andsupplementary materials. A graphical abstract image must be uploaded duringsubmission which should provide the reader with a visual description of the topic
covered in the article.

3.

The corresponding author should be clearly indicated.

4.

The abstract is limited to 350 words and should be informative and include principal
findings and conclusions. Please avoid abbreviations.

5.

The main text can have multiple free headings.

6.

High-resolution figures should be provided in the following format; PDF (preferred
format for diagrams), PNG (preferred format for photos or images), EPS ,TIFF, JPEG, BMP.
The graphical abstract should be approximately 920 × 300 pixels and should be
uploaded as a JPEG, PNG or SVG file.

7.

References must follow the Springer Basic style.

Correspondence
If you have any questions, please contact info@springeropen.com.

© EPS Steering Committee 2022 All rights reserved.
A Grant-in-Aid for Publication of Scientific Research Results (19HP1001) fromJapan Society for the Promotion of Science is used for printing.

Contents
L-band Synthetic Aperture Radar: Current and future applications to Earth sciences........................... Yosuke Aoki, Masato Furuya, Francesco De Zan, Marie-Pierre Doin, Michael Eineder, Masato Ohki and Tim J. Wright
Detection of triggered shallow slips caused by large earthquakes using L-band SAR interferometry........................................................................................................................................... Satoshi Fujiwara, Takayuki Nakano and Yu Morishita
Surface creep rate distribution along the Philippine fault, Leyte Island, and possible repeating of Mw ~ 6.5 earthquakes
on an isolated locked patch ................Yo Fukushima, Manabu Hashimoto, Masatoshi Miyazawa, Naoki Uchida and Taka’aki Taira
Surface deformation of Asama volcano, Japan, detected by time series InSAR combining persistent and distributed
scatterers, 2014–2018 .................................................................................................................Xiaowen Wang, Yosuke Aoki and Jie Chen
Determination of the dipping direction of a blind reverse fault from InSAR: case study on the 2017 Sefid Sang
earthquake, northeastern Iran .....................................................................................Nematollah Ghayournajarkar and Yo Fukushima
Landslide detection in mountainous forest areas using polarimetry and interferometric coherence................................................................................................................ Masato Ohki, Takahiro Abe, Takeo Tadono and Masanobu Shimada
Spatiotemporal behavior of a large-scale landslide at Mt. Onnebetsu-dake, Japan, detected by three L-band SAR satellites................................................................................................................................................................... Youichiro Takada and George Motono
Surface displacement revealed by L-band InSAR analysis in the Mayya area, Central Yakutia, underlain by continuous
permafrost..............................................................Takahiro Abe, Go Iwahana, Petr V. Efremov, Alexey R. Desyatkin, Takumi Kawamura,

1
5
5
6
6
7
7

Alexander Fedorov, Yuri Zhegusov, Kazuki Yanagiya and Takeo Tadono

8

Seasonal and transient surface displacements in the Kumamoto area, Japan, associated with the 2016 Kumamoto
earthquake: implications for seismic-induced groundwater level change.............................................................................................. Kazuya Ishitsuka, Takeshi Tsuji, Weiren Lin, Makoto Kagabu and Jun Shimada
Precursory ground deformation of the 2018 phreatic eruption on Iwo-Yama volcano, revealed by four-dimensional joint
analysis of airborne and spaceborne InSAR .....................................Shohei Narita, Taku Ozawa, Yosuke Aoki, Masanobu Shimada,

8

Masato Furuya, Youichiro Takada and Makoto Murakami

9

Postseismic deformation following the 2016 Kumamoto earthquake detected by ALOS-2/PALSAR-2.................................................................................................................................................................................................... Manabu Hashimoto 9
Surface deformation evolution in the Pearl River Delta between 2006 and 2011 derived from the ALOS1/PALSAR images............................................... Genger Li, Guangcai Feng, Zhiqiang Xiong, Qi Liu, Rongan Xie, Xiaoling Zhu, Shuran Luo and Yanan Du 10

Cover image: Fujiwara, S., Earth, Planets and Space 2020, 72:119 DOI: 10.1186/s40623-020-01239-6